Motor vehicles have a number of exterior lamps that are turned on and off by switches that are on the interiors of the vehicles. These lamps typically include headlamps, tail lamps, turn signal lamps, stop lamps, and marker lamps. An individual lamp may perform a single function or multiple functions, either by a single illumination element, or by multiple illumination elements.
One example of an exterior lamp that has multiple illumination elements is a dual-beam headlamp that has both a high-beam filament and a low-beam filament.
An example of an exterior lamp that performs multiple functions is a rear stop-turn signal lamp that will illuminate when the driver applies the vehicle service brakes and that will flash when the driver operates the turn signal switch to signal a turn in the direction to the side of the vehicle where the stop-turn signal lamp is located. The controls associated with such a dual-function lamp are arranged such that the turn signal function will override the stop function to enable the lamp to flash when the brakes are being applied.
Present-day motor vehicles have electrical systems that include one or more electrical system controllers, sometimes referred to as an ESC or ESC's. An ESC may be devoted to a particular vehicle system such as the body, chassis, or powertrain. An ESC comprises one or more electronic devices organized and arranged to receive data inputs, to process data according to programmed strategies and algorithms, and to provide data outputs. The ESC performs functions that provide information outputs as well as functions that provide control outputs.
The control functions include control of the exterior lamps in accordance with the status of controlling devices on the vehicle interior. Typical controlling devices are switches like a headlamp switch or turn signal switch. When a switch is turned on, a corresponding data input indicative of the switch status is issued to the ESC. The ESC acts on that input by issuing an output that results in performance of the function controlled by the switch. For example, when the brakes are applied, a stop lamp switch closes to apply a certain potential to a particular input of the ESC. The presence of that potential, which incidentally may be positive, negative, or ground depending on the particular ESC, at that input is understood by the ESC as a data signal calling for the stop lamps to illuminate. The ESC then issues a signal at a particular output to cause the stop lamps to illuminate.
The electronic devices that form an ESC, such as processors, typically operate at low current levels that are unsuited for directly supplying the electrical loads of devices like exterior lamps. Consequently, the ESC may be considered simply to interface the controlling devices, like stop lamp and turn signal switches, to the controlled devices, like the stop lamps and turn signal lamps, while additional devices like drivers, relays, or the like that can carry the load currents are present in circuit between the ESC and the various loads.
At various times it is desirable, or perhaps even mandated in some way, to check the operation of a vehicle's exterior lamps. Checking may be done at the factory as part of the check-out procedure for a new vehicle or after a vehicle has been placed in service.
For example, the operator or driver of a large vehicle like a heavy truck may want or require that various devices, including exterior lamps, be checked before embarking on a run. Because the controls for the exterior lamps are inside the cab while the exterior lamps themselves are on the outside where they may not be properly observed by a person inside the cab, the process of checking the exterior lamps requires more than one person, one inside the cab to operate the various controls and one or more persons outside to observe the lamps. Verbal and/or visual communication between the person inside the cab and the person or persons outside occurs as the check-out proceeds.
While an automated test capability may be available in certain vehicles for testing vehicle exterior lamps, insofar as the inventors are aware that capability tests only the lamps themselves, not the full circuitry that includes the controlling devices, because the automated test is embodied in an algorithm in the ESC that does not depend on the ESC receiving actual inputs from the controlling devices during exterior device testing. That automated test capability merely simulates the operation of the controlling devices internally of the ESC, typically, although not necessarily, in a pre-programmed sequence for operating the lamps in that sequence so as to enable a person observing the lamps to verify that they have illuminated in accordance with the sequence.
The test can show that a lamp which fails to illuminate when it should is either itself defective, or that the circuit between the lamp and the ESC is defective, or that the ESC is itself defective. However, the test has no way of disclosing a defect in a control device or in circuitry between a control device and the ESC because the function performed by the control device is merely simulated, instead of the control device itself being actuated. In other words, that test merely checks the functionality of the output portion of the entire circuit, not the input portion.